Flowmeter

ABSTRACT

A flowmeter for achieving a fluid flow rate value by using calibration curves on the basis of the output of a detection circuit using a bridge circuit ( 73 ) containing as constituent resistors respective temperature sensing elements of a flow rate detector containing a heating element ( 33 ) and a fluid temperature detector in an indirectly heated type flow rate sensor unit. The bridge circuit ( 73 ) varies the circuit characteristic value in plural steps by a multiplexer ( 731 ) for selectively connecting the output terminal and any one of the connection terminals between the in-series connected resistors. Plural calibration curves are provided in association with the steps of the circuit characteristic value, and any one of the plural calibration curves is selected in accordance with the step of the circuit characteristic value selected by the multiplexer ( 731 ). The flow rate range to be measured is set every calibration curve, and the multiplexer ( 731 ) is controlled in accordance with the fluid flow rate value thus achieved, and the calibration curve corresponding to the flow rate range to which the flow rate value belongs. According to this flowmeter, the flow rate can be measured with excellent precision over a board flow rate range.

TECHNICAL FIELD

The present invention relates to a fluid flow rate detecting technique,and particularly to a flowmeter for measuring the flow rate orintegrated flow amount of fluid flowing in a pipe. Furthermore, thepresent invention relates to a thermal type flowmeter such as anindirectly heated type flowmeter or the like, and further to a thermaltype flowmeter having a fluid temperature compensating function.

BACKGROUND TECHNIQUE

Various types have been known for a flowmeter [flow rate sensor] (orcurrent meter [flow velocity sensor]) for measuring the flow rate (orflow velocity) of various kinds of fluid, particularly liquid. Of thesetypes of flowmeters, a so-called thermal type (particularly, indirectlyheated type) flowmeter has been used because the price thereof is lower.

One of indirectly heated type flowmeters is designed and used so that asensor chip comprising a thin-film heating element and a thin-filmtemperature sensing element which are laminated on a substrate throughan insulating layer by using the thin film technique is disposed so asto enable the heat transfer between the sensor chip and fluid flowing ina pipe. The electrical characteristic of the temperature sensingelement, for example, the value of the electrical resistance is variedby supplying current to the heating element to heat the temperaturesensing element. The variation of the electrical resistance value (basedon increase of the temperature of the temperature sensing element) isvaried in accordance with the flow rate (flow velocity) of the fluidflowing in the pipe. This is because a part of the heating value of theheating element is transferred into the fluid, the heating value thusdiffused into the fluid is varied in accordance with the flow rate (flowvelocity), and the heating value supplied to the temperature sensingelement is varied in accordance with the variation of the heating valuediffused into the fluid, so that the electrical resistance value of thetemperature sensing element is varied. The variation of the electricalresistance value of the temperature sensing element is also varied inaccordance with the temperature of the fluid. Therefore, a temperaturesensing element for temperature compensation is installed in anelectrical circuit for measuring the variation of the electricalresistance value of the temperature sensing element to reduce thevariation of the flow rate measurement value due to the temperature ofthe fluid as much as possible.

With respect to the indirectly heated type flowmeter using the thin-filmelement as described above, JP(A)-11-118566 discloses an example of theindirectly heated type flowmeter. The flowmeter disclosed in thispublication uses an electrical circuit (detection circuit) containing abridge circuit to achieve the electrical output corresponding to a flowrate of fluid.

It is general that the output of the electrical circuit of the flowmeteris not in a simply proportional relationship with the flow rate value,and variation of the output of the electrical circuit to the flow ratevariation is large in an area where the flow rate value is small whilethe variation of the output of the electrical circuit to the flow ratevariation is small in an area where the flow rate value is large.Therefore, there is a problem that even when little error occurs onmeasured flow rate values due to the variation of the output of theelectrical circuit in the small flow rate value area, the error isincreased in the large flow rate value area (that is, the rate of theflow rate difference to be discriminable when the measurement is carriedout is increased).

In order to avoid this problem, it has been hitherto general that aflowmeter is prepared for each relatively narrow flow rate range and thecharacteristic value of the electrical circuit is properly set everyflow rate range. Therefore, if attention is paid to each individualflowmeter, it has a problem that the dynamic range of the flow ratemeasurement is small and the application of the indirectly heated typeflowmeter suffers restriction.

Therefore, an object of the present invention is to provide anindirectly heated type flowmeter which can perform a flow ratemeasurement with excellent precision over a broad flow rate range.

In the flowmeter disclosed in JP(A)-11-118566, the voltage to be appliedto the heating element is varied in accordance with the variation of theflow rate to thereby vary the heating state of the heating element sothat the temperature sensing element is kept to a predeterminedtemperature (heating state), and the flow rate value is achieved on thebasis of the voltage applied to the heating element at this time.

The environmental temperature at which the flowmeter is used is broad.For example, when the flowmeter is used in a cold district, thetemperature of the flowmeter may be kept under 5° C. or less. On theother hand, when the flowmeter is used in a hot district, thetemperature of the flowmeter may be kept at 35° C. or more. Even whenthe flowmeter is used in the same district, the environmentaltemperature of the flowmeter is varied in accordance with day and night.Accordingly, when the flow rate value is achieved on the basis of thevoltage to be applied to the heating element as described above, thereis a problem that the measurement value is varied in accordance with theenvironmental temperature, which is caused by variation of thecharacteristic of the electrical circuit of the flowmeter due to thetemperature variation.

The present invention has another object to improve the control of anapplied voltage to the heating element in the indirectly heated typeflowmeter as described above and achieve high precision and high controlresponse without complicating the circuit construction.

Further, the present invention has another object to prevent thevariation of the measurement value due to the environmental temperaturein the indirectly heated type flowmeter as described above, and furtherenhance the precision of the flowmeter.

When the flow rate detection is carried out by using the thermal typeflowmeter, the following problems occur due to the variation of thetemperature of fluid for which the flow rate is detected.

For example, in a case where a kerosene flow passage is formed by a pipeso as to extend from a kerosene tank disposed outdoors to keroseneburning equipment disposed indoors and a flowmeter is disposed in anindoor portion of the pipe, if there is a large difference between theoutdoor temperature and the indoor temperature (for example, thedifference in temperature may be equal to about 20° C. in the winterseason), kerosene remaining in the indoor portion of the pipe firstpasses through the flowmeter at the initial stage where use of thekerosene burning equipment is started, and after some amount of kerosenepasses through the flowmeter, kerosene existing in the outdoor portionof the pipe at the initial stage reaches the flowmeter to be detected inflow rate.

In most cases, a fluid temperature detecting unit containing atemperature sensing element for temperature compensation installed in afluid flow rate detecting circuit is disposed at a position differentfrom that of a fluid flow rate detecting unit, or even when they aredisposed to be near to each other, a heat-exchange portion of the fluidflow rate detecting unit at which heat exchange is actually carried outto detect the fluid flow rate is far away from a heat-exchange portionof the fluid temperature detecting unit at which heat exchange isactually carried out to detect the fluid temperature. In these cases, iffluid which quickly varies in temperature flows into the flowmeter asdescribed above, there appears temporarily such a state that the fluidtemperature when the heat-exchange with the fluid temperature detectingunit is carried out is different from the fluid temperature when theheat-exchange with the fluid flow rate detecting unit is carried out.Therefore, accurate temperature compensation cannot be performed andthus the precision of the fluid flow rate detection is reduced.

Therefore, the present invention has an object to provide a flowmeterwhich can accurately make a fluid temperature compensation and thusperform accurate flow rate detection even when the temperature of fluidflowing into the flowmeter quickly varies.

SUMMARY OF THE INVENTION

In order to attain the above objects, according to the presentinvention, there is provided a flowmeter having an indirectly heatedtype flow rate sensor unit in which a flow rate detector containing aheating element and a temperature sensing element for flow ratedetection is joined to a heat transfer member for flow rate detection, afluid flow rate value being achieved with calibration curves on thebasis of the output of a detection circuit using a bridge circuitcontaining the temperature sensing element for flow rate detection as aconstituent resistor, characterized in that the bridge circuit includescircuit characteristic value variation driving means for varying thecircuit characteristic value thereof in plural steps, plural calibrationcurves are provided in association with the respective steps of thecircuit characteristic value, any one of the plural calibration curvesis selected in conformity with the step of the circuit characteristicvalue selected by the circuit characteristic value variation drivingmeans, a fluid flow rate range to be measured is set every calibrationcurve, the overall measurement flow rate range is covered by the pluralfluid flow rate ranges, and the circuit characteristic value variationdriving means is controlled in accordance with the fluid flow rate valueachieved to use one of the calibration curves corresponding to the flowrate range to which the flow rate value belongs.

In an aspect of the present invention, the respective neighboring flowrate ranges are partially overlapped with each other, and the selectiveswitching from one of the two calibration curves corresponding to thetwo partially-overlapped flow rate ranges to the other calibration curveis carried out at the end portion of the one flow rate range.

In an aspect of the present invention, the flow rate sensor unit has afluid temperature detector containing a fluid temperature detectingtemperature sensing element and a fluid temperature detecting heattransfer member joined to the fluid temperature detector, and the bridgecircuit contains the fluid temperature detecting temperature sensingelement as a constituent resistor.

In an aspect of the present invention, the circuit characteristic valuevariation driving means is a multiplexer for selectively connecting anoutput terminal of the bridge circuit to any one of connection terminalsbetween any two neighboring resistors of plural resistors which areprovided to said bridge circuit so as to be connected to one another inseries.

In an aspect of the present invention, the circuit characteristic valuevariation driving means carries out a switch-ON/OFF operation ofswitches of a bypass which are connected in parallel to at least one ofplural resistors which are provided to the bridge circuit so as to beconnected in series to one another. In an aspect of the presentinvention, each of the switches comprises a field effect transistor.

In order to attain the above objects, according to the presentinvention, there is provided a thermal type flowmeter having a heatingelement and a flow rate detection circuit containing a temperaturesensing element for flow rate detection disposed so as to be affected bythe heating of the heating element and perform heat transfer from/tofluid, the heating of the heating element being controlled on the basisof a voltage applied to the heating element, the applied voltage to theheating element being controlled on the basis of the output of the flowrate detection circuit and the flow rate of the fluid being measured onthe basis of the applied voltage, characterized in that the appliedvoltage to the heating element is equal to the total voltage of a basevoltage the value of which is set every predetermined time period andinvariable within each predetermined time period, and an additionvoltage which has a fixed value and is variable in voltage applyingtime, a comparator for comparing the output of the flow rate detectingcircuit with a reference value is provided to output a binary signalhaving a first level indicating that the heating of the temperaturesensing element is insufficient and a second level indicating the othercases, the binary signal output from the comparator is sampled at apredetermined period to count the appearance frequency of the firstlevel every predetermined time period and achieve the count valuethereof every predetermined time period, the base voltage is adjusted sothat when the count value is within a predetermined range, the value ofthe base voltage in a subsequent predetermined time period is notchanged, when the count value is larger than the upper limit of thepredetermined range, the value of the base voltage in the subsequentpredetermined time period is increased by a predetermined step value andwhen the count value is smaller than the lower limit of thepredetermined range, the value of the base voltage in the subsequenttime period is reduced by the predetermined step value, and the additionvoltage is applied during only a time period when the binary signaloutput from the comparator has the first level.

In an aspect of the present invention, the addition voltage is set totwo times to four times of the step value of the base voltage. In anaspect of the present invention, the predetermined range of the countvalue has a lower limit value which is smaller than a half of thesampling frequency within the predetermined time period and larger thanzero, and has an upper limit value which is larger than a half of thesampling frequency within the predetermined time period and smaller thanthe sampling frequency.

In order to attain the above objects, according to the presentinvention, there is provided a thermal type flowmeter having a heatingelement and a flow rate detection circuit containing a temperaturesensing element for flow rate detection disposed so as to be affected bythe heating of the heating element and perform heat transfer from/tofluid, the heating of the heating element being controlled on the basisof a voltage applied to the heating element, the applied voltage to theheating element being controlled on the basis of the output of the flowrate detection circuit and the flow rate of the fluid being measured onthe basis of the applied voltage, characterized in that the appliedvoltage to the heating element is equal to the total voltage of a basevoltage the value of which is set every predetermined time period andinvariable within each predetermined time period, and an additionvoltage which has a fixed value and is variable in voltage applyingtime, a comparator for comparing the output of the flow rate detectingcircuit with a reference value is provided to output a binary signalhaving a first level indicating that the heating of the temperaturesensing element is insufficient and a second level indicating the othercases, the binary signal output from the comparator is sampled at apredetermined period to count the appearance frequency of the firstlevel every predetermined time period and achieve the count valuethereof every predetermined time period, the base voltage is adjusted sothat when the count value is within a predetermined range, the value ofthe base voltage in a subsequent predetermined time period is notchanged, when the count value is larger than the upper limit of thepredetermined range, the value of the base voltage in the subsequentpredetermined time period is increased by a predetermined step value andwhen the count value is smaller than the lower limit of thepredetermined range, the value of the base voltage in the subsequenttime period is reduced by the predetermined step value, the additionvoltage is applied during only a time period when the binary signaloutput from the comparator has the first level, and a data interpolatingcalculation is made by using an instantaneous flow rate converting tablecomprising plural individual calibration curves which indicate therelationship between the applied voltage to the heating element and theinstantaneous flow rate every discrete temperature value, therebyachieving an instantaneous flow rate value at an environmentaltemperature.

In an aspect of the present invention, the individual calibration curvesare created for discrete values of possible values of the voltage to beapplied to the heating element, and when the instantaneous flow ratevalue is achieved, a data interpolation calculation is carried out toachieve the instantaneous flow rate value corresponding to a voltagevalue applied to the heating element. In an aspect of the presentinvention, the discrete values are set to the minimum values of valueshaving the same high-order bit values of possible digital values of thevoltage to be applied to the heating element, and when the datainterpolation calculation is carried out, the instantaneous flow ratevalues corresponding to first discrete values having the same high-orderbit values as the voltage value applied to the heating element andsecond discrete values whose high-order bit values are larger than thatof the voltage value applied to the heating element by 1 are achieved bythe individual calibration curves.

In an aspect of the present invention, the addition voltage is set totwo times to four times of the step value of the base voltage.

In an aspect of the present invention, the predetermined range of thecount value has a lower limit value which is smaller than a half of thesampling frequency within the predetermined time period and larger thanzero, and has an upper limit value which is larger than a half of thesampling frequency within the predetermined time period and smaller thanthe sampling frequency.

In order to attain the above objects, according to the presentinvention, there is provided a flowmeter having an indirectly heatedtype flow rate sensor unit in which a flow rate detector containing aheating element and a temperature sensing element for flow ratedetection is joined to a heat transfer member for flow rate detection, afluid flow rate value being achieved with a calibration curve on thebasis of the output of a detection circuit containing the temperaturesensing element for flow rate detection, characterized in that thecalibration curve comprises three portions corresponding to three areasof the output value of the detection circuit, and the three portions arerepresented by quaternary functions which use the output of thedetection circuit as variables and are different in coefficient, a fluidflow rate value being achieved by using the portion of the calibrationcurve which corresponds to the area to which the output value of saiddetection circuit belongs.

In an aspect of the present invention, the calibration curve isrepresented as follows:f=a ₁ v ⁴ +b ₁ v ³ +c ₁ v ² +d ₁ v+e ₁  (0≦v<v ₁)f=a ₂ v ⁴ +b ₂ v ³ +c ₂ v ² +d ₂ v+e ₂ (v ₁ ≦v| ₂)f=a ₃ v ⁴ +b ₃ v ³ +c ₃ V ² +d ₃ v+e ₃ (v≦v)wherein f represents the fluid flow rate, v represents the output of thedetection circuit, and a₁, b₁, c₁, d₁, et; a₂, b₂, c₂, d₂, e_(z); a₃,b₃, c₃, d₃, e₃ represent coefficients.

In an aspect of the present invention, the detection circuit comprises abridge circuit. In an aspect of the present invention, the flow ratesensor unit has a fluid temperature detector containing a fluidtemperature detecting temperature sensing element and a fluidtemperature detecting heat transfer member joined to the fluidtemperature detector, and the detection circuit contains the fluidtemperature detecting temperature sensing element.

In order to attain the above objects, according to the presentinvention, there is provided a thermal type flowmeter which includes acasing member having a fluid flow passage extending from a fluid flow-inport to a fluid flow-out port, a flow rate detecting unit which issecured to the casing member and varies in electrical characteristicvalue in accordance with the flow of the fluid in the fluid flow passagethrough the heat exchange between the flow rate detecting unit and thefluid in the fluid flow passage, and a fluid temperature detecting unitwhich is secured to the casing member and varies in electricalcharacteristic value in accordance with the temperature of the fluidthrough the heat exchange between the fluid temperature detecting unitand the fluid in the fluid flow passage, the flow rate of the fluidbeing also detected on the basis of the electrical characteristic valueof the fluid temperature detecting unit, characterized in that a fluidresidence area is formed at the upstream side, with respect to the flowof the fluid, of each of the position at which the heat exchange betweenthe flow rate detecting unit and the fluid is carried out and theposition at which the heat exchange between the fluid temperaturedetecting unit and the fluid is carried out, the fluid residence areahaving a flow cross section which is five times or more, preferably tentimes or more, as large as the flow cross section at the position wherethe heat exchange between the flow rate detecting unit and the fluid iscarried out or at the position where the heat exchange between the fluidtemperature detecting unit and the fluid is carried out.

In order to attain the above objects, according to the presentinvention, there is provided a thermal type flowmeter which includes acasing member having a fluid flow passage extending from a fluid flow-inport to a fluid flow-out port, a flow rate detecting unit which issecured to the casing member and varies in electrical characteristicvalue in accordance with the flow of the fluid in the fluid flow passagethrough the heat exchange between the flow rate detecting unit and thefluid in the fluid flow passage, and a fluid temperature detecting unitwhich is secured to the casing member and varies in electricalcharacteristic value in accordance with the temperature of the fluidthrough the heat exchange between the fluid temperature detecting unitand the fluid in the fluid flow passage, a fluid-temperature-compensatedflow rate of the fluid being detected by a detection circuit containingthe flow rate detecting unit and the fluid temperature detecting unit,characterized in that a fluid residence area is formed at the upstreamside, with respect to the flow of the fluid, of each of the position atwhich the heat exchange between the flow rate detecting unit and thefluid is carried out and the position at which the heat exchange betweenthe fluid temperature detecting unit and the fluid is carried out, theflow velocity of the fluid at the fluid residence area being equal to ⅕or less, preferably 1/10 or less, of the flow velocity of the fluid atthe position where the heat exchange between the flow rate detectingunit and the fluid is carried out or at the position where the heatexchange between the fluid temperature detecting unit and the fluid iscarried out.

In an aspect of the present invention, the volume of the fluid residencearea is 50 times or more as large as the volume per unit length of thefluid flow passage in the fluid flow direction at the position where theheat exchange between the flow rate detecting unit and the fluid iscarried out or at the position where the fluid temperature detectingunit and the fluid is carried out.

In an aspect of the present invention, the fluid flow passage comprisesa first flow passage part intercommunicating with the fluid flow-inport, and a second flow passage part intercommunicating with the fluidflow-out port, at which the heat exchange between the flow ratedetecting unit and the fluid is carried out and the heat exchangebetween the fluid temperature detecting unit and the fluid is carriedout, the fluid residence area is located between the first flow passagepart and the second flow passage part, and the flow cross section of thefirst flow passage part is smaller than the flow cross section of thefluid residence area.

In an aspect of the present invention, the second flow passage part hasa part extending in parallel to the fluid residence area at the positionwhere the heat exchange between the flow rate detecting unit and thefluid is carried out and at the position where the heat exchange betweenthe fluid temperature detecting unit and the fluid is carried out.

In an aspect of the present invention, a filter is interposed at theintercommunication portion between the fluid residence area and thesecond flow passage part. In an aspect of the present invention, thecasing member is formed of metal. In an aspect of the present invention,the flow rate detecting unit is designed so that a heating element, aflow rate detecting temperature sensing element and a flow ratedetecting heat transfer member extending into the fluid flow passage arearranged so as to perform heat transfer thereamong, and the fluidtemperature detecting unit is designed so that a fluid temperaturedetecting temperature sensing element and a fluid temperature detectingheat transfer member extending into the fluid flow passage are arrangedso as to perform heat transfer therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an embodiment of a flowmeteraccording to the present invention;

FIG. 2 is a diagram showing a part of the construction of the embodimentof the flowmeter according to the present invention;

FIGS. 3A and 3B are schematic cross-sectional views showing a flow ratesensor unit of the embodiment of the flowmeter according to the presentinvention;

FIG. 4 is a perspective view showing the flow rate sensor unit of theembodiment of the flowmeter according to the present invention;

FIGS. 5A and 5B are schematic cross-sectional views showing amodification of the flow rate sensor unit shown in FIGS. 3A and 3B;

FIG. 6 is an exploded perspective view showing the construction of aflow rate detector;

FIG. 7 is an exploded perspective view showing the construction of afluid temperature detector;

FIG. 8 is a diagram showing an example of calibration curves in theflowmeter of the present invention;

FIG. 9 is a partial circuit diagram showing another embodiment of theflowmeter according to the present invention;

FIG. 10 is a circuit diagram showing an embodiment of the flowmeteraccording to the present invention;

FIG. 11 is a partial detailed diagram of the circuit diagram of FIG. 10;

FIG. 12 is a partial detailed diagram of the circuit diagram of FIG. 10;

FIG. 13 is a cross-sectional view showing a flow rate detection portionof the flowmeter;

FIG. 14 is a cross-sectional view showing a flow rate detecting unit;

FIG. 15 is a time chart showing heater voltage control;

FIG. 16 is a time chart showing variation of a heater voltage andcalculation of a flow rate value;

FIG. 17 is a circuit diagram showing an embodiment of the flowmeteraccording to the present invention;

FIG. 18 is a partial detailed diagram of the circuit diagram of FIG. 17;

FIG. 19 is a diagram showing an instantaneous flow rate convertingtable;

FIG. 20 is a flowchart showing the operation of a flow rate integratingcircuit of the flowmeter;

FIG. 21 is a diagram showing error measurement data of the flowmeter;

FIG. 22 is a schematic diagram showing a flow rate detection system ofthe flowmeter according to the present invention;

FIG. 23 is a cross-sectional view showing the flow rate detecting unitof the flowmeter according to the present invention;

FIG. 24 is a diagram showing an example of a calibration curve in theflowmeter according to the present invention;

FIG. 25 is a cross-sectional view showing an embodiment of the flowmeteraccording to the present invention;

FIG. 26 is a partial cross-sectional view showing the embodiment of theflowmeter according to the present invention;

FIG. 27 is a front view showing the embodiment of the flowmeteraccording to the present invention;

FIG. 28 is a right side view showing the embodiment of the flowmeteraccording to the present invention;

FIG. 29 is a bottom view of the embodiment of the flowmeter according tothe present invention when a lid member is removed;

FIG. 30 is a left side view showing the embodiment of the flowmeteraccording to the present invention;

FIG. 31 is a plan view showing the embodiment of the flowmeter accordingto the present invention; and

FIG. 32 is a schematic diagram showing a flow rate detection system ofthe embodiment of the flowmeter according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments according to the present invention will bedescribed hereunder with reference to the accompanying drawings.

FIG. 1 is a diagram showing the circuit construction of an embodiment ofa flowmeter according to the present invention, and FIG. 2 is a diagramshowing a partial construction of the flowmeter of FIG. 1.

FIGS. 3A and 3B are schematic cross-sectional views showing a flow ratesensor unit according to the embodiment, wherein FIG. 3A shows a statethat the flowmeter is secured to a flow passage member having a fluidflow passage, and FIG. 3B is a cross-sectional view taken along X-X ofthe flow rate sensor unit of FIG. 3A. FIG. 4 is a perspective viewshowing the flow rate sensor unit of the embodiment. FIGS. 5A and 5B areschematic cross-sectional views showing a modification of the flow ratesensor unit shown in FIGS. 3A and 3B, wherein FIG. 5B is across-sectional view taken along X-X of FIG. 5A. FIG. 6 is an explodedperspective view showing the construction of a flow rate detector, andFIG. 7 is an exploded perspective view showing the construction of afluid temperature detector. First, the construction of a flow ratesensor unit according to this embodiment will be described withreference to FIGS. 3A to 7. As shown in FIGS. 3A and 3B, a flow ratedetector 5 is joined to the surface of a fin plate 6 serving as a heattransfer member for flow rate detection, and a fluid temperaturedetector 9 is joined to the surface of a fin plate 10 serving as a heattransfer member for fluid temperature detection. The flow rate detector5, the fluid temperature detector 9 and parts of the fin plates 6, 10are accommodated in a housing 2.

As shown in FIG. 6, the flow rate detector 5 is designed in the form ofa chip by laminating, in the following order, a thin-film temperaturesensing element 31 for flow rate detection, an interlayer insulatingfilm 32, a thin-film heating element 33 with its electrodes 34, 35 and aprotection film 36 on a rectangular substrate of about 0.4 mm inthickness and about 2 mm in square formed of silicon, alumina or thelike and then forming a pad layer 37 so that the bonding portion of thethin-film temperature sensing element 31 for flow rate detection and theheating element electrodes 34, 35 are covered by the pad layer 37.

As the thin-film temperature sensing element 31 may be used a metalresistance film having a high and stable temperature coefficient such asplatinum (Pt), nickel (Ni) or the like which is patterned to have athickness of about 0.5 to 1 μm and have a desired shape, for example, ameandering shape. Alternatively, a manganese oxide-based NTC thermistoror the like may be used. Each of the interlayer insulating film 32 andthe protection film 36 may be formed of SiO₂ and have a thickness ofabout 1 μm. As the thin-film heating element 33 may be used a resistorpatterned to have a thickness of about 1 μm and have a desired shape,which is formed of Ni, Ni—Cr, Pt or cermet such as Ta—SiO₂, Nb—SiO₂ orthe like. The heating element electrode 34, 35 may be formed of a Nithin film having a thickness of about 1 μm, or both of a Ni thin film ofabout 1 μm in thickness and a gold (Au) thin film of about 0.5 amlaminated on the Ni thin film. As the pad layer 37 may be used an Authin film or Pt thin film of 0.2 mm×0.15 mm in area and about 0.1 μm inthickness.

As shown in FIG. 7, the fluid temperature detector 9 has substantiallythe same construction as the flow rate detector 5 except that theheating element 33, etc. are removed from the construction of the flowrate detector 5, that is, a thin-film temperature sensing element 31′for fluid temperature detection similar to the thin-film temperaturesensing element 31 for fluid temperature detection and a protection film36′ similar to the protection film 36 are laminated in this order on asubstrate 30′ similar to the substrate 30, and also a pad layer 37′ isformed so as to cover the bonding portion of the thin-film temperaturesensing element 31′ for fluid temperature detection, thereby finallyachieving the fluid temperature detector 9 as a chip.

One surface of the fin plate 6 (10) at one end portion thereof is joinedto the surface of the flow rate detector 5 (the fluid temperaturedetector 9) at the substrate 30 (30′) side thereof through a jointmember having excellent thermal conductivity. The fin plate 6, 10 maycomprise a rectangular plate of about 0.2 mm in thickness and about 2 mmin width which is formed of copper, duralumin, copper-tungsten alloy orthe like. Silver paste may be used as the joint member.

As shown in FIGS. 3A and 3B, the housing 2 of the sensor unit isaccommodated in a sensor unit arrangement portion formed in the flowpassage member 14, and the other end portions of the fin plates 6, 10extend into the fluid flow passage 13 formed in the fluid flow passagemember 14. The fin plates 6, 10 extend to pass through the center of thecross section in the fluid flow passage 13 having a substantiallycircular cross section. The fin plates 6, 10 are arranged along the flowdirection (indicated by an arrow in FIG. 1) of the fluid in the fluidflow passage 13, so that the heat exchange between the fluid and each ofthe flow rate detector 5 and the fluid temperature detector 9 can beexcellently carried out without greatly disturbing the fluid flow.

The housing 2 and the fluid flow passage member 14 may be formed ofsynthetic resin. The respective electrode terminals (pads) of the flowrate detector 5 and the fluid temperature detector 9 are connected tothe inner lead portions (the in-housing portions) of the respectiveleads 7, 11 by Au wires 8, 12. Each of the leads 7, 11 extend to theoutside of the housing 2 so as to be partially exposed to the outside,thereby forming an outer lead portion.

In FIGS. 3A and 3B, the flow rate detector 5, the fluid temperaturedetector 9, parts of the fin plates 6, 10 and the inner lead portionsare sealingly accommodated in the housing 2 by resin filling. However, aspace 23 may be formed in the housing 22 as shown in a modification ofFIGS. 5A and 5B.

Next, the circuit construction of the flowmeter of this embodimenthaving the sensor unit as described above will be described withreference to FIGS. 1 and 2.

As shown in FIG. 1, alternating power of 100V is used as a power supplysource, and DC voltages of +15V, −15V and +5V are output from a DCconverting circuit 71 by using the alternating power of 100V. The DCvoltage of +15V output from the DC converting circuit 71 is input to avoltage stabilizing circuit 72.

The stabilized DC voltage supplied from the voltage stabilizing circuit72 is supplied to a bridge circuit 73. As shown in FIG. 2, the bridgecircuit 73 contains the temperature sensing element 31 for flow ratedetection and resistors 74, 90 which are connected to one another inseries, and the temperature sensing element 31′ for temperaturecompensation and resistors 75, R1 to R7 which are connected to oneanother in series. The bridge circuit 73 is equipped with a multiplexer731 serving as circuit characteristic value variation driving means, andthe multiplexer 731 selectively connects the connection terminal b toone of the connection terminals c1 to c8 each of which is connected to apoint between the respective two neighboring resistors of the resistors75, R1 to R7. The characteristic value of the bridge circuit 73 can bevaried in plural steps by the selection of any one of the connectionterminals 1 to c8. The potential Va, Vb at the point a, b of the bridgecircuit 73 is input to a differential amplifying circuit 76 of variableamplification factor. The output of the differential amplifying circuit76 is input to an integrating circuit 77.

The output of the voltage stabilizing circuit 72 is supplied to thethin-film heating element 33 through a field effect transistor 81 forcontrolling the current to be supplied to the thin-film heating element33. That is, in the flow rate detector 5, the thin-film temperaturesensing element 31 executes the temperature sensing (detecting)operation on the basis of the heating of the thin-film heating element33 with being affected by the endothermic action of fluid to be detectedthrough the fin plate 6. As the result of the temperature sensingoperation is achieved the difference between the potential Va at thepoint of a and the potential Vb at the point of b in the bridge circuit73 shown in FIG. 2.

The value of (Va-Vb) is varied due to variation of the temperature ofthe temperature sensing element 31 for flow rate detection and thethin-film temperature sensing element 31′ for fluid temperaturedetection in accordance with the flow rate of the fluid. The value(Va-Vb) may be set to zero at a different fluid flow rate in accordancewith selection of one of the terminals c1 to c8 to be connected to theterminal b by the multiplexer 731. At these flow rates, the output ofthe differential amplifying circuit 76 is equal to zero, and thus theoutput of the integrating circuit 77 is equal to a fixed value.

The output of the integrating circuit 77 is input to a V/F convertingcircuit 78 to form a pulse signal having the frequency (for example,5×10⁻⁵ at maximum) corresponding to the voltage signal. The pulse signalhas a fixed pulse width (time width) (for example, a desired value from1 to 10 microseconds). For example, when the output of the integratingcircuit 77 is equal to 1V, a pulse signal having a frequency of 0.5 kHzis output. When the output of the integrating circuit 77 is equal to 4V,a pulse signal having a frequency of 2 kHz is output. The bridge circuit73, the differential amplifying circuit 76, the integrating circuit 77and the V/F converting circuit 78 constitute the detection circuit.

The output of the V/F converting circuit 77 is supplied to the gate of atransistor 81, and current is supplied to the thin-film heating element33 through the transistor 81 the gate of which is supplied with thepulse signal. Accordingly, the thin-film heating element 33 is suppliedwith a divided voltage of the output voltage of the voltage stabilizingcircuit 72 through the transistor 81 in the form of a pulse at thefrequency corresponding to the output value of the integrating circuit77, so that the current flows through the thin-film heating element 33intermittently to thereby heat the thin-film heating element 33. Thefrequency of the V/F converting circuit 77 is set on the basis ofhigh-precision clocks which are set on the basis of oscillation of atemperature-compensated type quartz oscillator 79.

The pulse signal output from the V/F converting circuit 77 is counted bya pulse counter 82. A microcomputer 83 converts the pulse count result(pulse frequency) to the corresponding flow rate (instantaneous flowrate) on the basis of a reference frequency generated in a referencefrequency generating circuit 80, and integrates the flow rate thusachieved with respect to the time, thereby calculating an integratedflow rate.

The selection of the connection between the connection terminal b andone of the connection terminals c1 to c8 through the multiplexer 731 iscontrolled by the microcomputer 83 as shown in FIG. 2. The selection ofthe connection terminals c1 to c8 by the microcomputer 83 and theconversion to the flow rate are performed as follows.

That is, calibration curves for the conversion to the flow rate arestored in a memory 84. FIG. 8 shows examples of the calibration curves.These calibration curves contain S₁, S₂, S₃, . . . , and thesecalibration curves are used in association with the circuitcharacteristic value steps when the connection terminals c1, c2, c3 . .. are selected by the multiplexer 731, respectively. The calibrationcurves S₁, S₂, S₃, . . . constitute a data table achieved by selectivelyconnecting the connection terminal b and each of the connectionterminals c1, c2, c3, . . . and, under this state, measuring the output(pulse frequency) of the pulse counter 82 every actual flow rate of thefluid.

In FIG. 8, the calibration curve S₁ is mainly used when the connectionterminal c1 of the multiplexer 731 is selected to measure a flow raterange from 0 to F₁₂, S₂ is mainly used when the connection terminal c2of the multiplexer 731 is selected to measure a flow rate range from F₁₁to F₂₂, S₃ is mainly used when the connection terminal c3 of themultiplexer 731 is selected to measure a flow rate range from F₂₁ toF₃₂, and so forth. Here, as shown in FIG. 8, F₁, <F₁₂<F₂₁<F₂₂<F₃₁<F₃₂,and the flow rate value F₁₁ corresponds to the output values fill, f₁₁₂of the calibration curves S₁, S₂ respectively, the flow rate value F₁₂corresponds to the output values f₁₂₁, f₁₂₂ of the calibration curvesS₁, S₂ respectively, the flow rate value F₂₁ corresponds to the outputvalues f₂₁₁, f₂₁₂ of the calibration curves S₂, S₃ respectively, theflow rate value F₂₂ corresponds to the output values f₂₂₁, f₂₂₂ of thecalibration curves S₂, S₃ respectively, and so forth. That is, theneighboring flow rate ranges are partially overlapped with each other,and the overall measuring flow rate range is covered by these flow rateranges.

The microcomputer 83 first instructs the multiplexer 731 to select aconnection terminal cn to measure a certain flow rate range [forexample, makes an instruction to select the connection terminal c2 tomeasure the flow rate range from F₁₁ to F₂₂] when the flow rate of thefluid to be detected is measured. Thereafter, the pulse frequencyachieved from the counter 82 is converted to the flow rate by using acalibration curve Sn [for example, the calibration curve S₂]. When theflow rate value thus achieved is within the flow rate rangecorresponding to the selected connection terminal cn [for example, fromF₁₁ to F₂₂], the selection of the connection terminal cn [for example,c2] by the multiplexer 731 is kept.

On the other hand, when the flow rate value achieved is out of the flowrate range corresponding to the selected connection terminal cn [out ofthe range from F₁₁ to F₂₂], the microcomputer instructs the multiplexer731 to select the connection terminal cm [for example, c3] in order tomeasure the flow rate range [for example, from F₂₁ to F₃₂] to which theflow rate value achieved belongs. Likewise, the pulse frequency achievedfrom the counter 82 is converted to the flow rate by using a calibrationcurve S₁ [for example, S₃]. When the flow rate value thus achieved iswithin the flow rate range [for example, from F₂₁ to F₃₂] correspondingto the selected connection terminal cm, the selection of the connectionterminal cm by the multiplexer 731 is kept. On the other hand, when theflow rate value thus achieved is out of the flow rate range [forexample, from F₂₁ to F₃₂] corresponding to the selected connectionterminal cm, the microcomputer instructs the multiplexer 731 to select aconnection terminal to measure a flow rate range to which the flow ratevalue thus achieved belongs.

Likewise, on the basis of the measured flow rate value achieved, themicrocomputer 83 controls the multiplexer 731 to achieve a bridgecircuit characteristic required to measure the flow rate value concernedat all times (specifically, select one of the connection terminals), andperforms the flow rate value measurement based on a proper calibrationcurve.

When some variation occurs in the flow rate while the flow rate ismeasured and thus the flow rate is out of the flow rate rangecorresponding to the selected calibration curve, the selection of thecurrent calibration curve is switched to the calibration curvecorresponding to a flow rate range which is adjacent to and partiallyoverlapped with the current flow rate range (the selection of theconnection terminal is switched under the control of the multiplexer731). Accordingly, the selective switching between the calibrationcurves for the neighboring flow rate ranges is carried out withdirectionality at the end portion of each flow rate range (for example,only the switching from the calibration curve S₃ to the calibrationcurve S₂ is carried out at the flow rate value F₂₁, and only theswitching from the calibration curve S₂ to the calibration curve S₃ iscarried out at the flow rate value F₂₂) as shown in FIG. 8. With thissetting, even when variation of the flow rate occurs in the neighborhoodof the switching flow rate value occurs, it is unnecessary toselectively switch the calibration curve frequently, and thus stabilityof the measurement can be kept.

As shown in FIG. 8, each of the calibration curves has a moderate slope(the rate of variation of the output pulse frequency to variation of theflow rate) in the flow rate range in which the calibration curve ismainly used, and the moderate flow rate variation with respect to theoutput variation can be implemented. Accordingly, in the flowmeter ofthis embodiment which is controlled to use the calibration curve S(indicated by a solid line in FIG. 8) constructed by predeterminedrespective flow rate range portions of the calibration curves, the flowrate measurement can be performed in a broad flow rate range withexcellent precision.

When the flow rate of the fluid is increased/reduced, the output of thedifferential amplifying circuit 76 is varied in polarity (varied inaccordance with the sign (positive or negative) of theresistance-temperature characteristic of the temperature sensing element31 for flow rate detection) and magnitude in accordance with the valueof (Va-Vb), and the output of the integrating circuit 77 is varied inaccordance with this variation of the output of the differentialamplifying circuit 76. The variation rate of the output of theintegrating circuit 77 can be adjusted by setting the amplificationfactor of the differential amplifying circuit 76. The responsecharacteristic of the control system is set by the integrating circuit77 and the differential amplifying circuit 76.

When the fluid flow rate is increased, the temperature of thetemperature sensing element 31 for flow rate detection is reduced.Therefore, such an output (higher voltage value) that the heating valueof the thin-film heating element 33 is increased (that is, the pulsefrequency is increased) can be achieved from the integrating circuit 77,and the bridge circuit 73 is set to the equilibrium state at the timepoint when the output of the integrating circuit is equal to the voltagevalue corresponding to the fluid flow rate.

On the other hand, when the fluid flow rate is reduced, the temperatureof the temperature sensing element 31 for flow rate detection isincreased. Therefore, such an output (lower voltage value) that theheating value of the thin-film heating element 33 is reduced (that is,the pulse frequency is reduced) can be achieved from the integratingcircuit 77, and the bridge circuit 73 is set to the equilibrium state atthe time point when the output of the integrating circuit 77 is equal tothe voltage corresponding to the fluid flow rate.

That is, in the control system of this embodiment, the frequency(corresponding to the heating value) of the pulse current to be suppliedto the thin-film heating element 33 is set so that the bridge circuit 73is set to the equilibrium state, and implementation of the equilibriumstate (the response of the control system) as described above can beperformed within 0.1 second, for example.

Accordingly, according to the flowmeter of this embodiment, even whenthe flow rate value to be detected is varied in a broad range and thusit is deviated from each flow rate range, a proper bridge circuitcharacteristic conformed with the flow rate range to which the flow ratevalue to be detected belongs can be immediately set, so that the flowrate measurement can be performed with high precision on the basis ofthe bridge circuit characteristic thus set.

The instantaneous flow rate and the integrated flow rate thus achievedare displayed on a display portion 25, and also transmitted to theoutside through a communication line comprising a telephone line orother networks. Further, the data of the instantaneous flow rate and theintegrated flow rate may be stored in the memory 84 if necessary.

In FIG. 1, reference numeral 85 represents a backup battery (forexample, cell).

According to the above-described embodiment, the pulse signal generatedin the V/F conversion circuit 78 is used to measure the flow rate, andit is easy to sufficiently reduce the error of the pulse signal due tothe temperature variation. Therefore, the errors of the flow rate valueand the integrated flow rate value achieved on the basis of the pulsefrequency can be reduced. Further, according to this embodiment, thecontrol of the current supply to the thin-film heating element 33 isperformed by ON/OFF based on the pulse signal generated in the V/Fconverting circuit 78. Therefore, the probability that a control errordue to the temperature variation occurs is extremely small.

Further, this embodiment uses a minute chip containing the thin-filmheating element and the thin-film temperature sensing element as theflow rate detector, so that the high-speed response as described abovecan be implemented and the precision of the flow rate measurement isexcellent.

FIG. 9 is a partial circuit diagram showing another embodiment of theflowmeter according to the present invention. In FIG. 9, the elementsand parts having the same functions as shown in FIGS. 1 to 8 arerepresented by the same reference numerals. In this embodiment, theconstruction of the bridge circuit 73 containing the circuitcharacteristic value variation driving means is different from that ofthe embodiment shown in FIGS. 1 to 8, however, the other portions aresubstantially the same as the embodiment shown in FIGS. 1 to 8.

In this embodiment, the bridge circuit 73 contains the in-seriesconnection between the temperature sensing element 31 for flow ratedetection and the resistor 74 and the in-series connection between thetemperature sensing element 31′ for temperature compensation andresistors 75, r0 to r3. The circuit characteristic value variationdriving means of this embodiment carries out the switch-on/off operationof a bypass containing field effect transistors FET1 to FET3 (switchingmeans) which are respectively connected to the in-series connectedresistors r1 to r3 of the bridge circuit in parallel. That is, switchingsignals from switching terminals SW1 to SW3 of a switching circuit 732controlled by the microcomputer 83 are input to the gates of the fieldeffect transistors FET1 to FET3, respectively. The field effecttransistors FET1 to FET3 are designed so that the source-drainresistance values thereof under the switch-ON state are sufficientlylower than r1 to r3 (for example, several tens mΩ) and the source-drainresistance values thereof under the switch-OFF state are sufficientlyhigher than r1 to r3 (for example, several MΩ). Accordingly, thecomposite resistance value of the in-series connected portion of theresistors r0 to r3 with the bypass in the bridge circuit 73 is varied asshown in the following Table 1 in accordance with the ON (for example,4V) or OFF (for example, 0V) state of the switching signals output fromthe switching terminals SW1 to SW3 when r0=10 Ω, r1=10 Ω, r2=20 Ω, r3=40Ω. TABLE 1 Composite resistance value of SW3 SW2 SW1 in-seriesconnection portion r0 to r3 ON ON ON 10 Ω ON ON OFF 20 Ω ON OFF ON 30 ΩON OFF OFF 40 Ω OFF ON ON 50 Ω OFF ON OFF 60 Ω OFF OFF ON 70 Ω OFF OFFOFF 80 Ω

The combination of the switching signals output from the switchingterminals SW1 to SW3 of the switching circuit 732 is controlled by themicrocomputer 83 as described above to vary the characteristic value ofthe bridge circuit in plural steps as in the case of the embodimentshown in FIGS. 1 to 8, and the flow rate can be measured in the samemanner.

FIG. 10 is a circuit diagram showing an embodiment of the flowmeteraccording to the present invention, and FIGS. 11 and 12 are partiallydetailed diagrams of FIG. 10. FIG. 13 is a cross-sectional view of aflow rate detection portion of the flowmeter according to theembodiment, and FIG. 14 is a cross-sectional view of a flow ratedetecting unit or flow rate sensor unit.

As shown in FIG. 13, a fluid flow passage 20 a is formed in a casingmember 20 formed of a material having excellent thermal conductivitysuch as aluminum or the like. The fluid flow passage 20intercommunicates with a fluid flow-in port (not shown) at the lowerside thereof and with a fluid flow-out port (not shown) at the upperside thereof, so that the fluid flows in from the fluid flow-in port,passes upwardly along the fluid flow passage 20 a and then flows outfrom the fluid flow-out port (as indicated by an arrow).

A flow rate detecting unit 24 and a fluid temperature detecting unit 26are secured to the casing member 20 so as to face the flow passage 20 a.As shown in FIG. 14, in the flow rate detecting unit 24, a flow ratedetector 42 is joined to the surface of a fin plate 44 serving as a heattransfer member through a joint member 46 having excellent thermalconductivity, and the electrode pad of the flow rate detector 42 and anelectrode terminal 48 are connected to each other by a bonding wire 50.The flow rate detector 42 and the bonding wire 50, a part of the finplate 44 and a part of the electrode terminal 48 are accommodated in ahousing 52 formed of synthetic resin. The flow rate detector 42 isdesigned as a chip by forming a thin-film temperature sensing elementand a thin-film heating element on a rectangular substrate so that thethin-film temperature sensing element and the thin-film heating elementare insulated from each other, the substrate being formed of silicon,alumina or the like to be about 0.4 mm in thickness and about 2 mm insquare.

The fluid temperature detecting unit 26 corresponds to the constructionachieved by using a fluid temperature detector in place of the flow ratedetector 42 in the flow rate detecting unit 24. In the fluid temperaturedetecting unit 26, “apostrophe (')” is affixed to the same referencenumerals for the members associated with those of the flow ratedetecting unit 24. The fluid temperature detector has the sameconstruction as the flow rate detector 42 except that the thin-filmheating element is removed from the flow rate detector 42.

As shown in FIG. 13, the end portions of the fin plates 44, 44′projecting from the housings 52, 52′ of the flow rate detecting unit 24and the fluid temperature detecting unit 26 extend into the flow passage20 a of the casing member 20. The fin plates 44, 44′ extend so as topass through the center in the cross section of the flow passage portion8 having substantially the circular cross section. The fin plates 44,44′ are arranged along the flowing direction of the fluid in the flowpassage 20 a, so that the heat transfer can be excellently performedbetween the fluid and each of the flow rate detector 42 and the fluidtemperature detector Δ′ without greatly affecting the flow of the fluid.

The tip portions of the electrode terminals 48, 48′ of the flow ratedetecting unit 24 and the fluid temperature detecting unit 26 penetratethrough a circuit board 60 secured to the casing member 20, and isconnected to a flowmeter electrical circuit portion formed on thecircuit board 60. A protection cover 62 is secured to the casing member20 to protect the circuit board 60.

As shown in FIG. 10, a DC voltage is supplied from a reference powersupply circuit 102 to a sensor circuit (detection circuit) 104. Thesensor circuit 104 comprises a bridge circuit as shown in FIG. 12. Thebridge circuit 104 comprises a flow rate detecting thin-film temperaturesensing element 104-1 of the flow rate detecting unit 24, a fluidtemperature compensating thin-film temperature sensing element 104-2 ofthe fluid temperature detecting unit 26 and resistors 104-3, 104-4. Thepotential Va, Vb at the point a, b of the bridge circuit 104 is input toa differential amplifying circuit (amplifier) 106, and the output of thedifferential amplifying circuit 106 is input to a comparator 108. Thecomparison result of the output voltage signal of the amplifier 106 anda reference voltage (Vref) is output as a binary signal from thecomparator 108. When the output signal of the amplifier 106 is lowerthan the reference voltage (Vref), the comparator 108 outputs a low (L)level [first level] signal, and when the output signal of the amplifier106 is equal to or higher than the reference voltage (Vref), thecomparator 108 outputs a high (H) level [second level] signal.

Further, as shown in FIG. 10, the DC voltage from the reference powersupply circuit 102 is supplied to a thin-film heating element 112 of theflow rate detecting unit 24 through a transistor 110 for controlling thecurrent to be supplied to the heating element 112. That is, in the flowrate detector 24, the thin-film temperature sensing element 104-1carries out the temperature sensing operation on the basis of theheating of the thin-film heating element 112 while being affected by theendothermic action of the fluid to be detected through the fin plate 44.As a temperature sensing result, the difference between the potential Vaat the point a of the bridge circuit 104 and the potential Vb at thepoint b of the bridge circuit 104 shown in FIG. 12 is achieved.

The value of (Va-Vb) is varied due to variation of the temperature ofthe flow rate detecting temperature sensing element 104-1 in accordancewith the flow rate of the fluid. By properly presetting thecharacteristic of the bridge circuit 104 and properly setting thereference voltage (Vref) of the comparator 108, the output voltagesignal of the amplifier 106 can be set to the reference voltage (Vref)of the comparator when the thin-film temperature sensing element 104-1is kept to a predetermined heating state (that is, the temperature ofthe thin-film temperature sensing element 104-1 is equal to apredetermined value). In other words, the reference voltage (Vref) ofthe comparator is set to be equal to the value of the output voltageachieved from the amplifier 106 when the thin-film temperature sensingelement 104-1 is kept under the predetermined heating state.

When the fluid flow rate is increased/reduced, the output of thecomparator 108 varies. The heating of the thin-film heating element (theheater for the sensor) is controlled by using the output of thecomparator 108. CPU 120 is used to control the heating of the thin-filmheating element 112 and further calculate the flow rate. The output ofthe comparator 108 is input through PLD 122 to a heater control circuit124 of CPU 120 as shown in FIG. 10. The output of the heater controlcircuit 124 is converted to an analog signal by a D/A converter 128, theanalog signal thus achieved is input to an amplifier 130 to beamplified, and then the output voltage signal of the amplifier 130 isinput to the base of the transistor 110. A signal is transmitted fromthe heater control circuit 124 to a flow rate integrating calculationcircuit 132 in CPU 120, and a calculation result, etc. are output fromthe flow rate integrating calculation circuit 132 to a display portion134, whereby necessary displays are made on the display portion 134.

As shown in FIG. 11, PLD 122 has a synchronizing circuit 122 a, an edgedetecting circuit 122 b and a 125-counter 122 c. The heater controlcircuit 124 has an “L” level counter 124 a, a comparison circuit 124 band a heater voltage circuit 124 c.

A clock signal is input from a 4 MHz clock circuit 136 to CPU 120. Theclock signal is converted to 1 MHz clock by a frequency-dividing circuit138 in CPU 120 and then input to the 125-counter 122 c in PLD 122 andthe “L” level counter 124 a in the heater control circuit 124.

The output of the comparator 108 is passed through PLD 122 and theninput to the “L” level counter 124 a to be sampled every 1 μsecond(predetermined period). The “L” level counter 124 a counts an appearancefrequency of “L” level within 125 μseconds (predetermined time period)set by the 125-counter 122 c. The data of the count value (count dataCD) thus achieved by the counter 124 a are input to the comparisoncircuit 124 b to be compared with a predetermined range. Thepredetermined range may has a lower limit value (for example, 43) whichis smaller than a half (62.5) of the sampling frequency (125) within thepredetermined time period of 125 μsec and larger than zero, and has anupper limit value (for example, 82) which is larger than a half of thesampling frequency within the predetermined time period of 125 μsec andsmaller than the sampling frequency (125).

In the heater voltage circuit 124 c, a control voltage [this term issometimes used in the same meaning as the heater applied voltage in thisspecification because it corresponds to an applied voltage to the heater112] input to the transistor 130 to control the applied voltage to theheater 112 for sensor is equal to the sum of a base voltage (Eb) andaddition voltage (Ec). The base voltage is selected from discrete valueswhich are preset at intervals of predetermined step value. The value ofthe base voltage is fixed within each predetermined time period, and theheating of the heater is roughly controlled by the base voltage. Theaddition voltage has a fixed value, however, the applying time period orapplying timing thereof is variable, so that the heating of the heateris finely controlled by the addition voltage. It is appropriate that theaddition voltage is set to a value which is from twice to four times ashigh as the step value of the base voltage.

The comparison circuit 124 b instructs the heater voltage circuit 124 cto keep the previous base voltage in the next predetermined time periodwhen the count data CD is not less than the lower limit value Nd and notmore than the upper limit value Nu. Further, when the count data CD isless than the lower limit value Nd, the comparison circuit 124 binstructs the heater voltage circuit 124 c to reduce the base voltagefrom the previous base voltage by 1 step value in the next predeterminedtime period. When the count data CD is more than the upper limit valueNu, the comparison circuit 124 b instructs the heater voltage circuit124 c to increase the base voltage from the previous base voltage by 1step value in the next predetermined time period.

The output of the comparator 108 is passed through PLD 122 and theninput to the heater voltage circuit 124 c. On the basis of the inputsignal, the heater voltage circuit 124 c allows application of theaddition voltage (Ec) during the period when the input signal is keptunder “L” level, and prohibits application of the addition voltage (Ec)during the other period.

The heater voltage control as described above will be described indetail with reference to the time chart of FIG. 15.

FIG. 15 shows the time-variation in the relationship between the outputsignal (the input signal to the comparator 108) of the amplifier 106connected to the bridge circuit 104 and the reference voltage (Vref) ofthe comparator 108, and also shows the time-variation of the outputsignal of the comparator 108. Further, FIG. 15 shows variation of thecount data CD input to the comparison circuit 124 b achieved in the “L”level counter 124 a every 125 μseconds, and also shows thetime-variation of the heater applied voltage (Eh) in association withthe variation of the count data CD. Further, FIG. 15 schematically showsthe time-variation of an actual flow rate in association with the timevariation of the heater applied voltage (Eh).

The lower limit and upper limit values Nd and Nu set in the comparisoncircuit 124 b are set to 43 and 82, respectively. In case of 43≦CD≦82,on the basis of the instruction from the comparison circuit 124 b,during the predetermined time period of 125 μseconds subsequent to thepredetermined time period at which the count data CD is achieved, thebase voltage Eb is not changed, but kept to the value at the just-beforepredetermined time period in the heater voltage circuit 124 c. In caseof CD<43, on the basis of the instruction from the comparison circuit124 b, during the predetermined time period of 125 μseconds subsequentto the predetermined time period at which the count data CD is achieved,the base voltage Eb is reduced by only 1 step voltage value (in thiscase, 10 mV) from the value at the just-before predetermined time periodin the heater voltage circuit 124 c. In case of CD>82, on the basis ofthe instruction from the comparison circuit 124 b, during thepredetermined time period of 125 μseconds subsequent to thepredetermined time period at which the count data CD is achieved, thebase voltage Eb is increased by only 1 step voltage value (in this case,10 mV) from the value at the just-before predetermined time period inthe heater voltage circuit 124 c.

On the other hand, in the heater voltage circuit 124 c, a prescribedaddition voltage (Ec: 30 mV in this case) is applied during the periodwhen the output signal of the comparator 108 is under “L” level, and noaddition voltage is applied during the period when the output signal ofthe comparator 108 is under “H” level.

As described above, according to this embodiment, on the basis of countdata CD achieved within a prescribed time period, the base voltagewithin the subsequent prescribed time period is properly set, and theaddition voltage applying time period is properly set in accordance withthe output of the comparator. By combining these two control operations(setting operations), the response of the control can be enhanced, theprecision of the flow rate measurement can be enhanced and the thermalhysteresis can be reduced with a simple device construction.

The predetermined time period, the predetermined period, the basevoltage step value, the addition voltage value and the other parametersmay be properly set in consideration of the predicted maximum variationof the flow rate so as to support this predicted maximum variation.

As described above, the heating of the thin-film heating element 112 iscontrolled so that the temperature of the flow rate detectingtemperature sensing element 104-1 is equal to a predetermined value(that is, the heating state of the flow rate detecting temperaturesensing element 104-1 is set to a predetermined state) irrespective ofthe variation of the fluid flow rate. At this time, the voltage (theheater applied voltage) applied to the thin-film heating element 112corresponds to the fluid flow rate, so that it is taken out as the flowrate output in the flow rate integration calculating circuit 132 shownin FIGS. 10 and 11. For example, the instantaneous flow rate is outputevery 0.5 second and the instantaneous flow rate thus output isintegrated to achieve the integrated flow rate.

That is, as shown in FIG. 11, the integration value (ΣEc) of theaddition voltage Ec applied for 0.5 second is achieved on the basis ofthe count data CD for each predetermined time period achieved in the “L”level counter 124 a, the integration value (ΣEb) of the base voltage Ebapplied for 0.5 second is achieved on the basis of the base voltagevalue Eb achieved in the heater voltage circuit 124 c, and the totalvalue (ΣEc+ΣEb=ΣEh) is achieved (see FIG. 16). This value is convertedto the instantaneous flow rate value by using the calibration curves(instantaneous flow rate conversion table) which are measured and storedin advance. This instantaneous flow rate conversion table is a tableindicating the relationship between the integration value of the heaterapplied voltage for 0.5 second and the flow rate value. Specifically,the instantaneous flow rate conversion table intermittently shows therelationship between the integration value of the heater applied voltageand the flow rate value, and thus data are complemented to achieve theflow rate value from the actually-achieved integration value of theheater applied voltage. The integrated flow rate value is obtained byintegrating the instantaneous flow rate values.

The output of the flow rate is displayed by the display portion 134. Onthe basis of the instruction from CPU 120, the instantaneous flow ratevalue and the integrated flow rate value may be properly stored in amemory, and these data may be transmitted to the outside through acommunication line such as a telephone line or other networks.

FIG. 17 is a circuit diagram showing an embodiment of the flowmeteraccording to the present invention, and FIG. 18 is a partially detaileddiagram of the flowmeter of FIG. 17.

This embodiment has the same construction as the embodiment shown inFIGS. 10 to 16 except that an environmental temperature measuringcircuit 140 and an A/D converter 142 shown in FIGS. 17 and 18 are added.The environmental temperature measuring circuit 140 is provided to theflowmeter electrical circuit portion (not shown) on the circuit board 60shown in FIG. 13, and measures the temperature (environmentaltemperature) at this position. The environmental temperature measuringcircuit 140 may be constructed by using a temperature sensing resistorsuch as a platinum resistor or the like, and outputs the electricalsignal corresponding to the environmental temperature (which is mainlydetermined by the effect of the external temperature and the temperatureof the fluid).

In this embodiment, the same operation as the embodiment shown in FIGS.10 to 16 is performed except the measurement of the environmentaltemperature and the processing using the measurement result.

According to this embodiment, in the same manner as the embodiment shownin FIGS. 10 to 16, the integration value (ΣEc) of the addition voltageEc applied for 0.5 second is achieved on the basis of the value of thecount data CD for each predetermined time period which is achieved bythe “L” level counter 124 a, the integration value (ΣEb) of the basevoltage Lb applied for 0.5 second is achieved on the basis of the basevoltage Eb achieved in the heater voltage circuit 124 c, and then thetotal value thereof (ΣEc+ΣEb=ΣEh) (see FIG. 16). This total value isequal to any one of discrete values (represented by digital values of 29bits in this embodiment). This value is converted to the instantaneousflow rate value by using the calibration curves (instantaneous flow rateconversion table) which are measured and stored in advance. Theinstantaneous flow rate conversion table is a data table indicating therelationship between the integration value of the heater applied voltagefor 0.5 second and the flow rate value.

In this embodiment, the instantaneous flow rate conversion tablecomprises plural individual calibration curves formed every discretetemperature value. FIG. 19 shows an example of the instantaneous flowrate conversion table as described above. Individual calibration curvesT_(1 to T) ₄ for four discrete temperature values t₁ to t₄ (5° C., 15°C., 25° C. and 35° C.) are shown in FIG. 19. In FIG. 19, eachcalibration curve is illustrated as a continuous line, however, thisillustration is used for convenience's sake of description. Actually,the association relationship between each of the discrete heater appliedvoltages (integration values for 0.5 second). . . E_(ARm−1), E_(ARm),E_(ARM+1), E_(ARm+2), . . . shown in FIG. 19 and the instantaneous flowrate is shown. In this embodiment, the instantaneous flow rateconversion table does not show the relationship for all the possibleheater applied voltage integration values. That is, the integrationvalues of these possible heater applied voltage are sectioned intoplural groups in order of the magnitude, and the minimum values of therespective groups are represented by . . . E_(ARm−1), E_(ARm),E_(ARm+1), E_(ARm+2), . . . . The minimum values of those values whichhave the same high-order 8 bits in digital values that possiblyrepresent the heater applied voltages may be used as the above discreterepresentative values. In this case, 256 representative values areprovided.

Further, as shown in FIGS. 17 and 18, an environmental temperature value(for example, represented by a digital value of 10 bits) t is input fromthe environmental temperature measuring circuit 140 through the A/Dconverter 142 to the flow rate integration calculating circuit 132.

In the flow rate integration calculating circuit 132, the datainterpolation calculation is carried out according to the procedureshown in FIG. 20 on the basis of the count data value CD, the basevoltage Eb and the environmental temperature value t by using theinstantaneous flow rate conversion table as described above to achievethe instantaneous flow rate value.

That is, the heater applied voltage value ΣEh (=ΣEc+ΣEb) correspondingto the total value of the integration value of the addition voltage Ecand the integration value of the base voltage Eb for 0.5 second is firstcalculated (S1).

Next, the individual calibration curves T_(n), T_(n+1) (in the exampleof FIG. 19, n=2; that is, T₂[t₂=15° C.], T₃[t₃=25° C.]) satisfyingt_(n)≦t<t_(n+1) for the environmental temperature value t measured (22°C. in the example of FIG. 19) are selected (S2).

Next, the voltage values E_(ARm) and E_(ARm)+1 satisfyingE_(ARm)≦ΣEh<E_(ARm+1) are achieved. That is, the representative valueE_(ARm) of the group having the value ([10110100] in the example of FIG.19) represented by the high-order 8 bits of ΣEh and the representativevalue E_(ARm+1) of the group having the value ([10110101] in the exampleof FIG. 19) achieved by adding the value of the high-order 8 bits of ΣEhwith “1” are achieved. The voltage values E_(ARm) and E_(ARm+1) areconverted to instantaneous flow rate values F_(b), F_(a); F_(B), F_(A)on the individual calibration curves T_(n), T_(n+1) (S3).

Next, the instantaneous flow rate values F_(ab), F_(AB) on T_(n),T_(n+1) corresponding to ΣEh are achieved from values F_(b), F_(a);F_(B), F_(A) by the data interpolating calculation. At this time, thefollowing equations (1), (2) are used (S4).F _(ab)=(F _(a) −F _(b)) (ΣEh−E _(ARm))/(E _(ARm+1) −E_(ARm))+F_(b)  (1)F_(AB)=(F_(A)−F_(B)) (ΣEh−E_(ARm))/(E_(ARm+1)−E_(ARm))+F_(B)  (2)

Next, the instantaneous flow rate value Ft corresponding to ΣEh for theenvironmental temperature value t is achieved from F_(ab), F_(AB) by thedata interpolating calculation. At this time, the following equation (3)is used (S5).Ft=(F _(ab) −F _(AB)) (t−T ₃)/(T ₂ −T ₃)+F _(AB)  (3)

By achieving the instantaneous flow rate value Ft at the environmentaltemperature with the data interpolating calculation as described above,volume of the data of the instantaneous flow rate conversion table canbe reduced. In addition, the instantaneous flow rate measurement can beperformed with extremely little measurement error due to theenvironmental temperature. FIG. 21 shows an example of the measurementresult of the measurement error (display error) every flow rate value,which was achieved by using the flowmeter of this embodiment. It isapparent from FIG. 21 that high precision within ±1% in error wasachieved.

In the flow rate integration calculating circuit 132, the instantaneousflow rate value achieved is also integrated to achieve the integratedflow rate value.

The flow rate outputs such as the instantaneous flow rate value and theintegrated flow rate value thus achieved are displayed on the displayportion 134. On the basis of the instruction from CPU 120, theinstantaneous flow rate value and the integrated flow rate value may beproperly stored in a memory, and further may be transmitted to theoutside through a communication line such as a telephone line or othernetworks.

FIG. 22 is a schematic diagram showing the overall construction of theflowmeter, particularly, the flow rate detection system of the flowmeteraccording to the present invention, and FIG. 23 is a cross-sectionalview showing the flow rate detecting unit.

First, the construction of a flow rate sensor unit of this embodimentwill be described with reference to FIG. 23. As shown in FIG. 23, in aflow rate detecting unit 204, a flow rate detector 205 is joined to thesurface of a fin plate 224 serving as a heat transfer member by jointmaterial 226 having excellent thermal conductivity, and an electrode padof the flow rate detector 205 and an electrode terminal 228 areconnected to each other through a bonding wire 220. Further, the flowrate detector 205 and the bonding wire 220, and a part of the fin plate224 and a part of the electrode terminal 228 are accommodated in asynthetic esin housing 212. The flow rate detector 205 has theconstruction as shown in FIG. 6.

A fluid temperature detecting unit 206 has the same construction as theflow rate detecting unit 204 except that a fluid temperature detector isused in place of the flow rate detector 205 in the flow rate detectingunit 204. In the fluid temperature detecting unit 206, the partscorresponding to those of the flow rate detecting unit 204 arerepresented by the same reference numerals affixed with apostrophe “'”.The fluid temperature detector has the same construction as shown inFIG. 7.

As shown in FIG. 22, the end portions of fin plates 224, 224′ projectingfrom the housings 212, 212″ of the flow rate detecting unit 204 and thefluid temperature detecting unit 206 extend into the fluid flow passage203 of the fluid flow passage member 202. The fin plates 224, 224″extend to pass through the center in the cross section of the fluid flowpassage 203 having a substantially circular cross section. The finplates 224, 224′ are arranged along the fluid flowing direction in thefluid flow passage 203, so that excellent heat transfer between each ofthe flow rate detector 205 and the fluid temperature detector and thefluid can be performed without greatly affecting the fluid flow.

A DC voltage V1 is applied from a power supply circuit (not shown) to abridge circuit 240. The bridge circuit 240 comprises a thin-filmtemperature sensing element 231 for flow rate detection of the flow ratedetecting unit 204, a thin-film temperature sensing element 231′ fortemperature compensation of the fluid temperature detecting unit 206 andresistors 243, 244. The potential Va, Vb at the point a, b of the bridgecircuit 240 is input to a differential amplifying/integrating circuit246.

A DC voltage V2 from the power supply circuit is supplied to a thin-filmheating element 233 of the flow rate detecting unit 204 through atransistor 250 for controlling current to be supplied to the thin-filmheating element 233. That is, in the flow rate detector 205, thethin-film temperature sensing element 231 carries out the temperaturesensing operation on the basis of the heating of the thin-film heatingelement 233 with being affected by the endothermic action of the fluidto be detected through the fin plate 224. As a result of the temperaturesensing is achieved the difference between the potential Va at the pointa of the bridge circuit 240 and the potential Vb at the point b of thebridge circuit 240 shown in FIG. 22.

The value of (Va-Vb) is varied due to variation of the temperature ofthe temperature sensing element 231 for flow rate detection inaccordance with the flow rate of the fluid. By properly setting theresistance values of the resistors 243, 244 of the bridge circuit 240 inadvance, the value of (Va-Vb) can be set to zero when the fluid flowrate is equal to a desired value (reference value). At the referenceflow rate, the output of the differential amplifying/integrating circuit246 is equal to a fixed value (the value corresponding to the referenceflow rate), and the resistance value of the transistor 250 is equal to afixed value. In this case, a divided voltage to be applied to thethin-film heating element 233 is also equal to a fixed value, and thusthe voltage at the point P at this time indicates the reference flowrate.

When the fluid flow rate is increased/reduced, the output of thedifferential amplifying/integrating circuit 246 varies in polarity(varied in accordance with positive/negative sign of theresistance-temperature characteristic of the temperature sensing element231 for flow rate detection) and magnitude, and the output of thedifferential amplifying/integrating circuit 246 is varied in accordancewith the variation in polarity and magnitude.

When the fluid flow rate is increased, the temperature of thetemperature sensing element 231 for flow rate detection is reduced, andthus the differential amplifying/integrating circuit 246 supplies thebase of the transistor 250 with such a control input that the resistancevalue of the transistor 250 is reduced to thereby increase the heatingvalue of the thin-film heating element 233 (that is, to increase thepower).

On the other hand, when the fluid flow rate is reduced, the temperatureof the temperature sensing element 231 for flow rate detectionincreases, and thus the differential amplifying/integrating circuit 246supplies the base of the transistor 250 with such a control input thatthe resistance value of the transistor 250 is increased to therebyreduce the heating value of the thin-film heating element 233 (that is,to reduce the power).

As described above, the heating of the thin-film heating element 233 isfeed-back controlled so that the temperature detected by the temperaturesensing element 231 for flow rate detection is equal to a target valueirrespective of the variation of the fluid flow rate. Further, thevoltage (the voltage at the point P) applied to the thin-film heatingelement 233 corresponds to the fluid flow rate, and thus it is taken outas an output of the flow rate.

The output of the flow rate of this detection circuit is A/D-convertedby an A/D converter 252, and then converted to the corresponding flowrate (instantaneous flow rate) by CPU 254. The flow rate thus achievedis integrated with respect to the time to calculate the integrated flowrate (integrated flow amount). The values of the instantaneous flow rateand the integrated flow rate can be displayed by an integrated flow ratedisplay portion 256, and stored in a memory 284. Further, these valuesmay be transmitted to the outside through a communication line such as atelephone line or other networks.

The conversion from the output of the detection circuit to the flow ratein CPU 254 is carried out as follows. The calibration curve forconversion to the flow rate is stored in the memory 284 in advance. Anexample of the calibration curve is shown in FIG. 24. The calibrationcurve is represented as follows:f=a ₁ v ⁴ +b ₁ v ³ +c ₁ v ² +d ₁ v+e ₁(0≦v<v ₁)f=a ₂ v ⁴ +b ₂ v ³ +c ₂ v ² +d ₂ v+e ₂(v ₁ ≦v<v ₂)f=a ₃ v ⁴ +b ₃ v ³ +c ₃ v ² +d ₃ v+e ₃(v ₂ ≦v)wherein f [liter/h] represents the fluid flow rate, v[V] represents theoutput of the detection circuit, and a₁, b₁, c₁, d₁, e₁; a₂, b₂, c₂, d₂,e₂; a₃, b₃, c₃, d₃, e₃ represents coefficients.

In the case shown in FIG. 24,v₁=7.0 [V]v₂=8.0 [V]a ₁=+1.99933E−1b ₁=−4.84409E+0c ₁=+4.44365E+1d ₁=−1.82380E+2e ₁=+2.81911E+2a ₂=+3.45600E−1b ₂=−8.77327E+0c ₂=+8.40224E+1d ₂=−3.58917E+2e ₂=+5.75936E+2a ₃=+6.55492E+0b ₃=−2.13636E+2c ₃=+2.61702E+3d ₃=−1.42694E+4e ₃=+2.92043E+4

Accordingly, it is sufficient to store only the function style off=av⁴+bv³+cv²+dv+e, two threshold values v₁, v₂ serving as boundaries ofthree areas of the output values of the detection circuit (the firstarea of 0≦v<v ₁, the second area of v₁≦v<v₂, and the third area ofv₂≦v), and the values of a to e (a, to e₁, a₂ to e₂, a₃ to e₃) everyarea as the content of the calibration curve to be stored in the memory284, and thus the capacity of the memory 284 may be small.

FIG. 24 is a graph in which actual measurement values of the flow rateare plotted. These measurement values show the relationship between theoutput value of the detection circuit of the flowmeter when fluid ismade to flow into the flowmeter of this embodiment and the flow ratevalue achieved by actually measuring the volume of the fluid flown inthe flowmeter, and it is apparent from FIG. 24 that these measurementvalues excellently meet the calibration curve.

The technical background to explain that the measurement valuesexcellently meet the calibration curve will be described. The flow ratemeasurement can be also performed with excellent precision by using acalibration curve represented by one function over all the area of theoutput values of the detection circuit. However, in this case, six-orderor higher-order function styles are needed and the numerical calculationis extremely complicated. Therefore, according to the present invention,the area of the output values of the detection circuit is divided intothree parts, and the calibration curves which have differentcoefficients, but are represented by the same function style are usedfor all these three parts, whereby a four-order function style can beused as the function style. In addition, the flow rate measurement canbe performed with excellent precision without increasing the memorycapacity so much.

Accordingly, the memory area used when the calibration curve isindividually set for each of plural environmental temperature values canbe prevented from being greatly increased, and this makes it easy tomeasure the environmental temperature and use a proper calibration curve(if necessary, extrapolation is carried out with use of two calibrationcurves) based on the environmental temperature thus measured, therebyperforming the higher-precision flow rate measurement.

The calibration curve as described above can be created by determiningfive coefficients of the above function style for each area by using theleast squares method on the basis of the actual measurement as shown inFIG. 24. The threshold value v₁ may be set so that the flow rate valueis within the range from 0.5 to 2.0, and the threshold value v₂ may beset so that the flow rate value is within the range from 4.0 to 12.0.With this setting, the calibration curve which excellently meets theactual measurement values as shown in FIG. 24 can be achieved.

In CPU 254, one of the three areas to which the output v of thedetection circuit belongs is specified, and then the calculation usingthe function having the coefficients corresponding to the area thusspecified is made to achieve the flow rate value f.

As described above, in the flowmeter of this embodiment, the flow ratemeasurement can be performed with high precision even when the flow ratevalue to be detected varies in a broad range.

Further, according to this embodiment, the minute chip containing thethin-film heating element and the thin-film temperature sensing elementis used as the flow rate detector. Therefore, the high response asdescribed above can be implemented, and the precision of the flow ratemeasurement can be enhanced.

FIG. 25 is a cross-sectional view showing an embodiment of the flowmeteraccording to the present invention, and FIG. 26 is a partialcross-sectional view of the flowmeter of this embodiment. FIG. 27 is afront view of the flowmeter of this embodiment, FIG. 28 is a right sideview of the flowmeter of this embodiment, FIG. 29 is a bottom view ofthe flowmeter of this embodiment when some parts are removed, FIG. 30 isa left side view of the flowmeter of this embodiment, and FIG. 31 is aplan view of the flowmeter of this embodiment. FIG. 25 is an A-A′cross-sectional view of FIG. 30, and FIG. 26 is a B-B′ partialcross-sectional view of FIG. 27.

In these figures, three portions 304, 306, 308 constituting a fluid flowpassage are formed in a casing member 302 formed of material havingexcellent thermal conductivity such as aluminum or the like. The flowpassage portion 304 intercommunicates with a fluid flow-in port 314, andthe flow passage portion 308 intercommunicates with a fluid flow-outport 316. The fluid flowing from the fluid flow-in port 314 into theflow passage portion 304 passes through the flow passage portion 306 andthe flow passage portion 308 and then flows out from the fluid flow-outport 316 (in the flowing direction as indicated by an arrow). The flowpassage portion 306 constitutes a fluid residence area. A lid member 303is detachably mounted at the lower portion of the casing member 302, andthe lid member 303 constitutes a part of the casing member 302.

The flow passage portion 304 extends in the horizontal direction, theflow passage portion 306 extends in the vertical direction, and the flowpassage portion 308 comprises a vertical portion 308 a extending in thevertical direction and a horizontal portion 308 b extending in thehorizontal direction. A fluid supply source side pipe is connected tothe fluid flow-in port 314, and a fluid demand side pipe is connected tothe fluid flow-out port 316.

A male screw 310 is detachably screwed in the casing member 302 so as toclose the port intercommunicating with the upper portion of the flowpassage portion 306. A filter 312 including non-woven fabric comprisingglass fiber, plastic fiber or the like which is held by a proper holdermay be interposed in the intercommunication portion between the flowpassage portion 306 and the flow passage portion 308.

A flow rate detecting unit 324 and a fluid temperature detecting unit326 are secured to the casing member 302 so as to face the verticalportion 308 a of the flow passage portion 308. The flow rate detectingunit 324 has the construction as shown in FIG. 23. The fluid temperaturedetecting unit 326 has the same construction as the flow rate detectingunit 324 except that a fluid temperature detector is used in place ofthe flow rate detector. The fluid temperature detector has the sameconstruction except that the thin-film heating element is removed fromthe flow rate detector.

The end portions of fin plates 344, 344′ projecting from the housings352, 352′ of the flow rate detecting unit 324 and the fluid temperaturedetecting unit 326 extend into the vertical portion 308 a of the flowpassage portion 308 of the casing member 302. The fin plates 344, 344′extend to pass through the center in the cross section of the flowpassage portion 308 having the substantially circular cross section. Thefin plates 344, 344′ are arranged along the flow direction of the fluidin the flow passage portion 308, so that heat transfer can beexcellently performed between each of the flow rate detector 342 and thefluid temperature detector 342′ and the fluid without greatly affectingthe flow of the fluid.

FIG. 29 is a bottom diagram when the lid member 303 described above isremoved, and shows the flow passage portion 306 and the vertical portion308 a of the flow passage portion 308. In this embodiment, as shown inFIGS. 29 and 25, the flow passage portion (fluid residence area) 306 isformed so that the cross section thereof is sufficiently larger than thecross section of the flow passage portion 308. The cross section of theflow passage portion 306 is set to be five times or more, preferably tentimes or more as large as that of the flow passage portion 308, Thevolume of the flow passage portion 306 is larger than the volume perunit length of the vertical portion 308 a of the flow passage portion308 at which the flow rate detecting unit 324 and the fluid temperaturedetecting unit 326 are located. The volume of the flow passage portion306 is preferably 50 times or more, more preferably 100 times or more,as large as the volume per unit length of the vertical portion 308 a.

As described above, the flow passage portion 306 is located at theupstream side, with respect to the fluid flowing direction, of thevertical portion 308 a of the flow passage portion 308 at which the heatexchange for the flow rate detection is carried out, and it constitutesan area where the fluid flowing into the flow passage portion 308 staystemporarily. The fluid flow velocity at the flow passage portion 306 issmaller than that at the vertical portion 308 a of the flow passageportion 308, and is preferably equal to ⅕ or less, more preferably 1/10or less, of the fluid flow velocity at the vertical portion 308 a.

Further, the vertical portion 308 a of the flow passage portion 308extends in parallel to and proximately to the flow passage portion 306,and thus it is disposed to be liable to suffer thermal influence of thefluid in the flow passage portion 306.

The cross section of the flow passage portion 304 is smaller than thecross section of the flow passage portion 306, and it is set to the samelevel as the cross section of the flow passage portion 308. Accordingly,the fluid flow velocity in the flow passage portion 304 is the samelevel as the fluid flow velocity in the flow passage portion 308.

FIG. 32 is a schematic diagram showing a flow rate detection system of athermal flowmeter according to this embodiment. A DC voltage is appliedfrom a constant voltage circuit 402 to a bridge circuit (detectioncircuit) 404. The bridge circuit 404 comprises a flow rate detectingthin-film temperature sensing element 404-1 of a flow rate detectingunit 324, a temperature compensating thin-film temperature sensingelement 404-2 of a fluid temperature detecting unit 326 and variableresistors 404-3, 404-4. The potential Va, Vb at the point a, b of thebridge circuit 404 is input to a differential amplifying circuit 406,and the output of the differential amplifying circuit 406 is input to anintegrating circuit 408.

The DC voltage from a power supply source is supplied to a thin-filmheating element 412 of the flow rate detecting unit 324 through atransistor 410 for controlling current to be supplied to the thin-filmheating element 412. That is, in the flow rate detector of the flow ratedetecting unit 324, the thin-film temperature sensing element 404-1carries out the temperature sensing operation on the basis of theheating of the thin-film heating element 412 with being affected by theendothermic action of the fluid to be detected through the fin plate344. As a result of the temperature sensing operation, the differentialbetween the potential Va at the point a of the bridge circuit 404 andthe potential Vb at the point b of the bridge circuit 404 shown in FIG.32 is achieved.

The value of (Va-Vb) is varied due to variation of the temperature ofthe flow rate detecting temperature sensing element 404-1 in accordancewith the flow rate of the fluid. By properly setting the resistancevalues of the resistors 404-3, 404-4 of the bridge circuit 404 inadvance, the value of (Va-Vb) can be set to zero when the fluid flowrate is equal to a desired value (reference value). At the referenceflow rate value, the output of the integrating circuit 408 is equal to afixed value (the value corresponding to the reference flow rate value),and the resistance value of the transistor 410 is equal to a fixedvalue. In this case, a divided voltage to be applied to the thin-filmheating element 412 is also equal to a fixed value, and thus the voltageat the point P at this time indicates the reference flow rate value.

When the fluid flow rate is increased/reduced, the output of thedifferential amplifying circuit 406 varies in polarity (varied inaccordance with positive/negative sign of the resistance-temperaturecharacteristic of the flow detecting temperature sensing element 404-1)and magnitude, and the output of the integrating circuit 408 is variedin accordance with the variation in polarity and magnitude of the outputof the differential amplifying circuit 406.

When the fluid flow rate is increased, the temperature of the flow ratedetecting temperature sensing element 404-1 is reduced, and thus theintegrating circuit 408 supplies the base of the transistor 410 withsuch a control input that the resistance value of the transistor 410 isreduced to thereby increase the heating value of the thin-film heatingelement 412 (that is, to increase the power).

On the other hand, when the fluid flow rate is reduced, the temperatureof the flow rate detecting temperature sensing element 404-1 increases,and thus the integrating circuit 408 supplies the base of the transistor410 with such a control input that the resistance value of thetransistor 410 is increased to thereby reduce the heating value of thethin-film heating element 412 (that is, to reduce the power).

As described above, the heating of the thin-film heating element 412 isfeed-back controlled so that the temperature detected by the flow ratedetecting temperature sensing element 404-1 is equal to a target valueirrespective of the variation of the fluid flow rate. Further, thevoltage (the voltage at the point P) applied to the thin-film heatingelement 412 corresponds to the fluid flow rate, and thus it is taken outas an output of the flow rate.

As in the case of the above embodiment, the flow rate output is properlyA/D-converted by the A/D converter, and subjected to operationprocessing such as integration, etc. by CPU, and then the flow rate isdisplayed by the display portion. On the basis of the instruction fromCPU, the instantaneous flow rate and the integrated flow rate can beproperly stored in the memory. Further, these data may be transmitted tothe outside through a communication line such as a telephone line orother networks.

In this embodiment, since the flow passage portion 306 constitutes thefluid residence area, the fluid flow velocity at the flow passageportion 306 is low, and even when the temperature of the fluid flowingfrom the flow passage portion 304 into the flow passage portion 306varies sharply, the fluid newly supplied into the flow passage portion306 is mixed with the fluid which has already existed in the flowpassage portion 306 before the temperature variation occurs, and thusthere exists a time margin for averaging of the fluid temperature, sothat the temperature variation of the fluid supplied to the flow passageportion 308 is moderated. In addition, the casing member 302′ is formedof metal having excellent thermal conductivity, so that even when thetemperature of the fluid flowing into the fluid flow passage of thecasing member 302 varies sharply, the averaging of the temperature ofthe fluid in the flow passage is promoted by thermal conduction of thecasing member 302, so that the effect of the sharp variation of thetemperature of the flow-in fluid is moderated.

As described above, according to this embodiment, the temperaturevariation of the fluid in the vertical portion 308 a of the flow passageportion 308 at which the flow rate detecting unit 324 and the fluidtemperature detecting unit 326 are located is moderated. Therefore, evenwhen the temperature of the flow-in fluid varies sharply, the fluidtemperature detected by the fluid temperature detecting unit 326 issubstantially equal to the temperature of the fluid for which the flowrate is detected in the flow rate detecting unit 324, so that the fluidtemperature can be surely compensated and the precision of the flow ratedetection can be enhanced. The fluid temperature variation in thevertical portion 308 a of the flow passage portion 308 at which the flowrate detecting unit 324 and the fluid temperature detecting unit 326 arelocated is moderated, so that the operation of the control system can bestabilized, and from this viewpoint, the flow rate detection precisioncan be enhanced.

INDUSTRIAL APPLICABILITY

As described above, according to the flowmeter of the present invention,the flow rate can be measured with excellent precision over a broad flowrate range.

According to the present invention, by combining the two types ofcontrol operation, one of which is to properly set, on the basis of thecount value achieved within a predetermined time period, the basevoltage within the subsequent predetermined time period, and the otherof which is to properly set the applying period of the addition voltagein accordance with the output of the comparator, the response of theheater control can be enhanced, the precision of the flow ratemeasurement can be enhanced and the thermal hysteresis can be reducedwithout complicating the circuit construction.

Further, according to the present invention, the data interpolationcalculation is carried out to achieve the instantaneous flow rate valueat the environmental temperature, thereby reducing the data volume ofthe instantaneous flow rate conversion table, and the variation of themeasurement value due to the environmental temperature is prevented toperform the extremely high-precision flow rate measurement.

Still further, according to the flowmeter of the present invention, theflow rate can be measured with excellent precision over a board flowrate range without increasing the capacity of the memory for storing thecalibration curves so much.

Still further, according to the present invention, the fluid residencearea is formed at the upstream of the flow rate detecting unit and thefluid temperature detecting unit in the fluid flow passage, whereby thefluid temperature compensation can be surely performed even when thetemperature of flow-in fluid varies sharply, thereby enhancing theprecision of the flow rate detection.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. A thermal type flowmeter having a heating element and aflow rate detection circuit containing a temperature sensing element forflow rate detection disposed so as to be affected by the heating of theheating element and perform heat transfer from/to fluid, the heating ofthe heating element being controlled on the basis of a voltage appliedto the heating element, the applied voltage to the heating element beingcontrolled on the basis of the output of the flow rate detection circuitand the flow rate of the fluid being measured on the basis of theapplied voltage, characterized in that the applied voltage to saidheating element is equal to the total voltage of a base voltage thevalue of which is set every predetermined time period and invariablewithin each predetermined time period, and an addition voltage which hasa fixed value and is variable in voltage applying time, a comparator forcomparing the output of said flow rate detecting circuit with areference value is provided to output a binary signal having a firstlevel indicating that the heating of said temperature sensing element isinsufficient and a second level indicating the other cases, the binarysignal output from said comparator is sampled at a predetermined periodto count the appearance frequency of the first level every predeterminedtime period and achieve the count value thereof every predetermined timeperiod, the base voltage is adjusted so that when the count value iswithin a predetermined range, the value of the base voltage in asubsequent predetermined time period is not changed, when the countvalue is larger than the upper limit of the predetermined range, thevalue of the base voltage in the subsequent predetermined time period isincreased by a predetermined step value and when the count value issmaller than the lower limit of the predetermined range, the value ofthe base voltage in the subsequent time period is reduced by thepredetermined step value, and the addition voltage is applied duringonly a time period when the binary signal output from the comparator hasthe first level.
 8. The thermal type flowmeter as claimed in claim 7,wherein the addition voltage is set to two times to four times of thestep value of the base voltage.
 9. The thermal type flowmeter as claimedin claim 7, wherein the predetermined range of the count value has alower limit value which is smaller than a half of the sampling frequencywithin the predetermined time period and larger than zero, and has anupper limit value which is larger than a half of the sampling frequencywithin the predetermined time period and smaller than the samplingfrequency.
 10. A thermal type flowmeter having a heating element and aflow rate detection circuit containing a temperature sensing element forflow rate detection disposed so as to be affected by the heating of theheating element and perform heat transfer from/to fluid, the heating ofthe heating element being controlled on the basis of a voltage appliedto the heating element, the applied voltage to the heating element beingcontrolled on the basis of the output of the flow rate detection circuitand the flow rate of the fluid being measured on the basis of theapplied voltage, characterized in that the applied voltage to saidheating element is equal to the total voltage of a base voltage thevalue of which is set every predetermined time period and invariablewithin each predetermined time period, and an addition voltage which hasa fixed value and is variable in voltage applying time, a comparator forcomparing the output of said flow rate detecting circuit with areference value is provided to output a binary signal having a firstlevel indicating that the heating of said temperature sensing element isinsufficient and a second level indicating the other cases, the binarysignal output from said comparator is sampled at a predetermined periodto count the appearance frequency of the first level every predeterminedtime period and achieve the count value thereof every predetermined timeperiod, the base voltage is adjusted so that when the count value iswithin a predetermined range, the value of the base voltage in asubsequent predetermined time period is not changed, when the countvalue is larger than the upper limit of the predetermined range, thevalue of the base voltage in the subsequent predetermined time period isincreased by a predetermined step value and when the count value issmaller than the lower limit of the predetermined range, the value ofthe base voltage in the subsequent time period is reduced by thepredetermined step value, the addition voltage is applied during only atime period when the binary signal output from the comparator has thefirst level, and a data interpolating calculation is made by using aninstantaneous flow rate converting table comprising plural individualcalibration curves which indicate the relationship between the appliedvoltage to said heating element and the instantaneous flow rate everydiscrete temperature value, thereby achieving an instantaneous flow ratevalue at an environmental temperature.
 11. The thermal type flowmeter asclaimed in claim 10, wherein the individual calibration curves arecreated for discrete values of possible values of the voltage to beapplied to said heating element, and when the instantaneous flow ratevalue is achieved, a data interpolation calculation is carried out toachieve the instantaneous flow rate value corresponding to a voltagevalue applied to said heating element.
 12. The thermal type flowmeter asclaimed in claim 11, wherein the discrete values are set to the minimumvalues of values having the same high-order bit values of possibledigital values of the voltage to be applied to said heating element, andwhen the data interpolation calculation is carried out, theinstantaneous flow rate values corresponding to first discrete valueshaving the same high-order bit values as the voltage value applied tosaid heating element and second discrete values whose high-order bitvalues are larger than that of the voltage value applied to said heatingelement by 1 are achieved by the individual calibration curves.
 13. Thethermal type flowmeter as claimed in claim 10, wherein the additionvoltage is set to two times to four times of the step value of the basevoltage.
 14. The thermal type flowmeter as claimed in claim 10, whereinthe predetermined range of the count value has a lower limit value whichis smaller than a half of the sampling frequency within thepredetermined time period and larger than zero, and has an upper limitvalue which is larger than a half of the sampling frequency within thepredetermined time period and smaller than the sampling frequency.
 15. Aflowmeter having an indirectly heated type flow rate sensor unit inwhich a flow rate detector containing a heating element and atemperature sensing element for flow rate detection is joined to a heattransfer member for flow rate detection, a fluid flow rate value beingachieved with a calibration curve on the basis of the output of adetection circuit containing the temperature sensing element for flowrate detection, characterized in that the calibration curve comprisesthree portions corresponding to three areas of the output value of saiddetection circuit, and the three portions are represented by quaternaryfunctions which use the output of said detection circuit as variablesand are different in coefficient, a fluid flow rate value being achievedby using the portion of the calibration curve which corresponds to thearea to which the output value of said detection circuit belongs. 16.The flowmeter as claimed in claim 15, wherein the calibration curve isrepresented as follows:f=a ₁ V+b ₁ v+c ₁ v ² +d ₁ v+e ₁(0<v<v ₁)f=a ₂ v ⁴ +b ₂ v ³ +c ₂ v ² +d ₂ v+e ₂ (v ₁ <v<v ₂)f=a ₃ v ⁴ +b ₃ v ³ +c ₃ v ² +d ₃ v+e ₃ (v ₂ ≦v) wherein f represents thefluid flow rate, v represents the output of the detection circuit, anda₁, b₁, c₁, d₁, e₁; a₂, b₂, c₂, d₂, e₂; a₃, b₃, c₃, d₃, e₃ representcoefficients.
 17. The flowmeter as claimed in claim 15, wherein saiddetection circuit comprises a bridge circuit.
 18. The flowmeter asclaimed in claim 15, wherein said flow rate sensor unit has a fluidtemperature detector containing a fluid temperature detectingtemperature sensing element and a fluid temperature detecting heattransfer member joined to said fluid temperature detector, and saiddetection circuit contains said fluid temperature detecting temperaturesensing element.
 19. A thermal type flowmeter which includes a casingmember having a fluid flow passage extending from a fluid flow-in portto a fluid flow-out port, a flow rate detecting unit which is secured tothe casing member and varies in electrical characteristic value inaccordance with the flow of the fluid in the fluid flow passage throughthe heat exchange between the flow rate detecting unit and the fluid inthe fluid flow passage, and a fluid temperature detecting unit which issecured to the casing member and varies in electrical characteristicvalue in accordance with the temperature of the fluid through the heatexchange between the fluid temperature detecting unit and the fluid inthe fluid flow passage, the flow rate of the fluid being also detectedon the basis of the electrical characteristic value of the fluidtemperature detecting unit, characterized in that a fluid residence areais formed at the upstream side, with respect to the flow of the fluid,of each of the position at which the heat exchange between the flow ratedetecting unit and the fluid is carried out and the position at whichthe heat exchange between the fluid temperature detecting unit and thefluid is carried out, the fluid residence area having a flow crosssection which is five times or more as large as the flow cross sectionat the position where the heat exchange between said flow rate detectingunit and the fluid is carried out or at the position where the heatexchange between said fluid temperature detecting unit and the fluid iscarried out.
 20. The thermal type flowmeter as claimed in claim 19,wherein the flow cross section of the fluid residence area is ten timesor more as large as the flow cross section at the position where theheat exchange between said flow rate detecting unit and the fluid iscarried out or at the position where the heat exchange between saidfluid temperature detecting unit and the fluid is carried out.
 21. Thethermal type flowmeter as claimed in claim 19, wherein the volume ofsaid fluid residence area is 50 times or more as large as the volume perunit length of the fluid flow passage in the fluid flow direction at theposition where the heat exchange between said flow rate detecting unitand the fluid is carried out or at the position where said fluidtemperature detecting unit and the fluid is carried out.
 22. The thermaltype flowmeter as claimed in claim 19, wherein said fluid flow passagecomprises a first flow passage part intercommunicating with said fluidflow-in port, and a second flow passage part intercommunicating withsaid fluid flow-out port, at which the heat exchange between said flowrate detecting unit and the fluid is carried out and the heat exchangebetween said fluid temperature detecting unit and the fluid is carriedout, said fluid residence area is located between said first flowpassage part and said second flow passage part, and the flow crosssection of said first flow passage part is smaller than the flow crosssection of said fluid residence area.
 23. The thermal type flowmeter asclaimed in claim 22, wherein said second flow passage part has a partextending in parallel to said fluid residence area at the position wherethe heat exchange between said flow rate detecting unit and the fluid iscarried out and at the position where the heat exchange between saidfluid temperature detecting unit and the fluid is carried out.
 24. Thethermal type flowmeter as claimed in claim 22, wherein a filter isinterposed at the intercommunication portion between said fluidresidence area and said second flow passage part.
 25. The thermal typeflowmeter as claimed in claim 19, wherein said casing member is formedof metal.
 26. The thermal type flowmeter as claimed in claim 19, whereinsaid flow rate detecting unit is designed so that a heating element, aflow rate detecting temperature sensing element and a flow ratedetecting heat transfer member extending into said fluid flow passageare arranged so as to perform heat transfer thereamong, and said fluidtemperature detecting unit is designed so that a fluid temperaturedetecting temperature sensing element and a fluid temperature detectingheat transfer member extending into said fluid flow passage are arrangedso as to perform heat transfer therebetween.
 27. A thermal typeflowmeter which includes a casing member having a fluid flow passageextending from a fluid flow-in port to a fluid flow-out port, a flowrate detecting unit which is secured to the casing member and varies inelectrical characteristic value in accordance with the flow of the fluidin the fluid flow passage through the heat exchange between the flowrate detecting unit and the fluid in the fluid flow passage, and a fluidtemperature detecting unit which is secured to the casing member andvaries in electrical characteristic value in accordance with thetemperature of the fluid through the heat exchange between the fluidtemperature detecting unit and the fluid in the fluid flow passage, afluid-temperature-compensated flow rate of the fluid being detected by adetection circuit containing the flow rate detecting unit and the fluidtemperature detecting unit, characterized in that a fluid residence areais formed at the upstream side, with respect to the flow of the fluid,of each of the position at which the heat exchange between said flowrate detecting unit and the fluid is carried out and the position atwhich the heat exchange between said fluid temperature detecting unitand the fluid is carried out, the flow velocity of the fluid at saidfluid residence area being equal to ⅕ or less of the flow velocity ofthe fluid at the position where the heat exchange between the flow ratedetecting unit and the fluid is carried out or at the position where theheat exchange between the fluid temperature detecting unit and the fluidis carried out.
 28. The thermal type flowmeter as claimed in claim 27,wherein said fluid residence area is formed so that the flow velocity ofthe fluid is equal to 1/10 or less of the flow velocity of the fluid atthe position where the heat exchange between the flow rate detectingunit and the fluid is carried out or at the position where the heatexchange between the fluid temperature detecting unit and the fluid iscarried out.
 29. The thermal type flowmeter as claimed in claim 27,wherein the volume of said fluid residence area is 50 times or more aslarge as the volume per unit length of the fluid flow passage in thefluid flow direction at the position where the heat exchange betweensaid flow rate detecting unit and the fluid is carried out or at theposition where said fluid temperature detecting unit and the fluid iscarried out.
 30. The thermal type flowmeter as claimed in claim 27,wherein said fluid flow passage comprises a first flow passage partintercommunicating with said fluid flow-in port, and a second flowpassage part intercommunicating with said fluid flow-out port, at whichthe heat exchange between said flow rate detecting unit and the fluid iscarried out and the heat exchange between said fluid temperaturedetecting unit and the fluid is carried out, said fluid residence areais located between said first flow passage part and said second flowpassage part, and the flow cross section of said first flow passage partis smaller than the flow cross section of said fluid residence area. 31.The thermal type flowmeter as claimed in claim 30, wherein said secondflow passage part has a part extending in parallel to said fluidresidence area at the position where the heat exchange between said flowrate detecting unit and the fluid is carried out and at the positionwhere the heat exchange between said fluid temperature detecting unitand the fluid is carried out.
 32. The thermal type flowmeter as claimedin claim 30, wherein a filter is interposed at the intercommunicationportion between said fluid residence area and said second flow passagepart.
 33. The thermal type flowmeter as claimed in claim 27, whereinsaid casing member is formed of metal.
 34. The thermal type flowmeter asclaimed in claim 27, wherein said flow rate detecting unit is designedso that a heating element, a flow rate detecting temperature sensingelement and a flow rate detecting heat transfer member extending intosaid fluid flow passage are arranged so as to perform heat transferthereamong, and said fluid temperature detecting unit is designed sothat a fluid temperature detecting temperature sensing element and afluid temperature detecting heat transfer member extending into saidfluid flow passage are arranged so as to perform heat transfertherebetween.